THESIS
2023
1 online resource (ix, 59 pages) : illustrations (some color)
Abstract
This project is an experimental study of novel unconventional superconductivity observed in
different devices. In the first part, we demonstrate that an unconventional superconducting state
can be observed in monolayer NbSe
2 of presumably topological nature. Ising superconductivity
in transition metal dichalcogenides (TMD) such as 2H-NbSe
2 allows them to sustain superconductivity
under high magnetic field above the Pauli limit with quasiparticle spins pinned firmly
to the direction perpendicular to the basal plane. We use field-angle-resolved magnetoresistance
experiments for fields applied in different directions strictly parallel to the basal plane to measure
the symmetry of the superconducting order parameter. The results agrees with theoretical
predictions of the combination of a no...[
Read more ]
This project is an experimental study of novel unconventional superconductivity observed in
different devices. In the first part, we demonstrate that an unconventional superconducting state
can be observed in monolayer NbSe
2 of presumably topological nature. Ising superconductivity
in transition metal dichalcogenides (TMD) such as 2H-NbSe
2 allows them to sustain superconductivity
under high magnetic field above the Pauli limit with quasiparticle spins pinned firmly
to the direction perpendicular to the basal plane. We use field-angle-resolved magnetoresistance
experiments for fields applied in different directions strictly parallel to the basal plane to measure
the symmetry of the superconducting order parameter. The results agrees with theoretical
predictions of the combination of a nodal topological superconducting phase and a nematic superconducting
phase near the upper critical field, a six-fold symmetry superposed on a two-fold
symmetry. We also measured six-layer NbSe
2 grown on hexagonal boron nitride, for which
there is no anisotropy, suggesting that the anisotropy occurs solely in monolayer samples. Another
measurement of NbSe
2 was done on a bulk device. It shows a 4-fold symmetry which does
not agree with our expectations and therefore stimulates further experiments under more controlled
conditions. In the second part, TaNb
0.6ZrHfTi
0.4 has been measured. The experimental
results show that this high-entropy alloy superconductor is an isotropic s-wave superconductor
Post a Comment